1. Field of the Invention
The present invention relates to a technology for preventing the occurrence of sink marks and silver streaks in injection foam molding of a thermoplastic resin.
2. Description of the related art
In injection foam molding of a thermoplastic resin, molding conducted under ordinary conditions results in formation of silver-white streaks called silver streaks on the surface of the resulting molded article. Therefore, such conventional ordinary injection foam molding is not suitable for the production of products required to have a good appearance, such as interior parts of automobiles. There is known a method of setting the temperature of a cylinder of an injection machine to be low in order to avoid the formation of silver streaks. However, too low a temperature may result in insufficient foaming.